One of the factors or problems encountered in electrostatic printing or xerography in office copiers, facsimile machines and printers in which the image is fused on the paper under heat and pressure is that the process tends to cause a curl to be formed in the paper.
Curled paper is difficult to handle in a receiver for the sheets. Ideally the sets should be neat with edges aligned and easy to handle by an operator or in finishing apparatus in which the set may be stitched or stapled.
The curl problems with paper stem from the treatment of the sheets in the processor. A sheet of normal paper is taken from a supply source, such as a cassette or feeder, in an environment in which the paper is subject to humidity and absorbs a certain amount of moisture. The sheet is processed past a photo conductor where powder or liquid ink is applied to produce an image, and then the sheet is passed through a fuser and subjected to heat and pressure between rollers, with the result that normal, flat sheets are caused to curl. Curled sheets received in a collator or sorter in bins cause failure of the device due to jamming or mis-sorting of sheets and the bin capacity of the receiver is reduced. In addition, curled sheets do not tend to form neat stacks or sets when received in a simple receiver may, as in the case of some printers or copiers and facsimile machines.
In efforts to minimize curl problems in copiers and printers, the feed rolls may be modified or bins made larger, but there has been, prior to the invention described in my pending application Ser. No. 122,145 filed Nov. 17, 1987, no way to remove the curl from paper sheets by returning them to their original, normal flat condition, without requiring the use of complex positively driven rolls with large power consumption and tracking or the problems resulting from the use of pressure plates or springs and the like, wrinkling of sheets or smearing of print.
The device of the aforesaid application is very useful in conjunction with most copier, printer and facsimile machines. However, when such machines are not attended and/or multiple users are producing sets of different printed material, the different sets are indiscretely stacked one on the other causing manual problems in set or job separation upon removal from the receiver.
It is known that sets of sheets forming a copy of a document may be offset by angularly or laterally offsetting or shifting the sheet feed rolls or by laterally offsetting the receiver tray. Such offsetting devices are generally complicated and require considerable space.
In the modern day facsimile machines, space is at a premium and curling of sheets, as described above, is a severe problem due to the fact that the predominance of facsimile machines store paper on a tight roll.